Low noise amplifiers (LNAs) are widely used in front-end receivers in various wireless communication devices. These LNA devices are used for boosting power of received signals without introducing significant noise or distortion on the received signals. LNAs are variously coupled to other front-end receiver components, such as antennas, preselectors, mixers and switching networks, in different configurations for different receiver architectures. The use and topology of LNAs, and the receiver architecture within which the LNAs are integrated, vary for various communication devices, such as two-way radios, mobile radios and cell phones.
The ability for communication devices to communicate over several frequency bands is becoming increasingly prevalent. Present multi-band receivers utilize band select switches, in conjunction with LNAs and preselectors, to select a signal of particular frequency band for demodulation. Some receivers support as many as five bands (VHF, UHF1, UHF2, 700 MHz and 800 MHz) which can result in excessive loss due to the required switching. These losses can degrade receiver sensitivity and may result in intermodulation distortion. Furthermore, the receivers utilizing band select switches cannot be used to simultaneously demodulate signals of different frequency bands. Parts count, board area, power consumption, controller and logic complexity, and cost also present challenges when designing multi-band receivers.
Approaches have been suggested to overcome the utilization of band select switches. A resistive combiner may be used instead of switches to combine signals of different frequency bands from LNAs. While the resistive combiner reduces the logic complexity, it also results in front-end insertion loss and receiver sensitivity degradation. Additionally, using the resistive combiner, instead of a band select switch, does not significantly reduce the parts count or board area of a communication device.
Accordingly, it would be desirable to have an LNA capable of providing multi-band frequency operation without the aforementioned issues.
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